Photothermal heterogeneous oxidation of ethanol over Pt/TiO2

Photothermal catalytic oxidation of ethanol over TiO2 and Pt/TiO2 has been investigated. Platinum was deposited on the titania using both photoreduction and adsorption of the PtCl62- anion. The nominal weight loadings of Pt were less than 1 wt%. Thermal contributions to ethanol oxidation over Pt could be distinguished from photo-contributions to ethanol oxidation over TiO2 by comparing illuminated and dark reactions under the same conditions. A significant photothermal synergistic effect was seen for Pt/TiO2 catalysts. The activity for complete oxidation to CO2 is much greater than the contribution from photo-oxidation over TiO2 plus thermal oxidation over Pt. Experiments were conducted to investigate the mechanistic nature of the synergistic effect. The synergistic effect was found to be sensitive to preparation conditions, with photoreduced catalysts having higher activities compared to thermally reduced catalysts prepared by adsorption of the PtCl62- anion: The differences between the photo and thermally reduced Pt/TiO2 are attributed to differing extents of etching of the TiO2 surface by the acidic solution of chloroplatinic acid. An experiment with layered beds of Pt/TiO2 and TiO2 showed that adding unetched TiO2 to etched Pt/TiO2 could improve CO2 production. The photothermal synergistic enhancement of CO2 production appears to be caused primarily by gas phase transport of intermediates between the two catalyst phases in a mixed series-parallel kinetic pathway. Increased levels of acetaldehyde produced by photo-oxidation over TiO2 can lead to CO2 production by thermal reaction of the acetaldehyde over Pt. (C) 1998 Academic Press.